Methods of preparing cationic layer compounds, cationic layer compounds prepared thereby, and methods of use therefor

ABSTRACT

A method of preparing a modified cationic layer compound which includes providing a layer compound of the general formula (I): 
     
       
         [E e Z z D d V v (OH − ) x ](A n− ) a .qH 2 O  (I) 
       
     
     wherein E represents one or more monovalent alkali metal cations, e represents a number of from 0 to about 2, Z represents one or more divalent metal cations, z represents a number of from 0 to about 6, D represents one or more trivalent metal cations, d represents a number of from 0 to about 3, V represents one or more tetravalent metal cations, v represents a number of from 0 to about 1, (A n− ) represents an acid anion wherein n represents an integer of from 1 to 3, q represents a number of from about 1 to about 10, and wherein x&gt;a and e+2z+3d+4v=x+na; subjecting the layer compound to crystallization to provide a resultant material; and subjecting the resultant material to steam drying at a temperature of from about 200° C. to about 260° C. for a period of time of from about 3 to about 6 hours, said steam drying comprising passing a source of steam continuously over the resultant material at a rate of from about 0.001 to about 10 moles of water per hour, per kilogram of the resultant material; is described. Cationic layer compounds made by the disclosed process, and uses therefor, are also described.

BACKGROUND OF THE INVENTION

Halogenated plastics or molding compounds produced therefrom are knownto have a tendency toward degradation or decomposition reactions if theyare exposed to thermal stress or come into contact with high energyradiation, for example ultraviolet light. To counteract this there arecustomarily incorporated into them heavy metal compounds based, forexample, on lead, barium and/or cadmium. However, from the viewpoint ofoccupational health, there is a requirement to replace these absolutelyeffective stabilizers with substances which are less hazardous tohealth. As alternatives to the heavy metal compounds, for examplecalcium soaps and zinc soaps may be considered as stabilizers, but thesedo not achieve the efficiency of said heavy metal compounds, so that toincrease their stabilizing action costabilizers are required.

German Patent DE-C-30 19 632 (Kyowa Chemical Ind.) describes the use ofhydrotalcites to inhibit the thermal or UV-induced degradation ofhalogenated thermoplastic resins. In this patent, results of studies arereported which indicate that if hydrotalcites which are readilyavailable on the market are incorporated, for example, into vinylchloride resins, these hydrotalcites accelerate the dechlorination ofthe resins on heating or even cause a decomposition, black coloration orfoam formation of the resins. In addition, it has been found that thesehydrotalcites have poor dispersibility in the resins and adverselyaffect the rheological properties of the resins during the deformationand the appearance of the finished molded bodies. These research resultsare due to the small crystal size of the customary hydrotalcites andalso to the high specific BET surface area of at least about 50 m²/g andthe water coating of the hydrotalcite particles. Accordingly, it isproposed in German Patent DE-C-30 19 632 to use hydrotalcites having alarge crystal size and having a specific BET surface area of no morethan 30 m²/g. If desired, the hydrotalcites can be coated with ananionic surface-active compound such as sodium stearate.

European Patent Application EP-A-189 899 (Kyowa Chemical Ind.) alsodescribes resin compositions which comprise hydrotalcites havingspecific BET surface areas less than 30 m²/g. This European patentapplication discloses that the hydrotalcites can be modified with estersof higher fatty acids, anionic surface-active compounds and couplingagents of the silane or titanium types in order to improve thecompatibility of the hydrotalcite with the plastic compounds. Thehydrotalcites are to be modified in accordance with EP-A-189 899 bymechanical mixing of hydrotalcites with the modifying agents in pure ordissolved form.

According to DE-C-33 06 822 (Giulini Chemie), hydrotalcites of theformula [Mg₆Al₂(OH)₁₂] (CO₃)₂.xH₂—where x≧2—are obtained by reactingaluminum hydroxide with magnesium hydroxide or magnesium oxide in thepresence of basic magnesium carbonate as carbonate ion donor at atemperature of from 50° C. to 100° C. and subsequent spray-drying fromthe suspension. Aluminum hydroxide is used in particular in the form of“active” aluminum hydroxide.

U.S. Pat. No. 4,656,156 (Aluminum Company of America) describes a methodof producing hydrotalcite, with the aluminum component used being thealuminate liquor of the Bayer process. The Bayer liquor is reacted with“active” magnesium oxide, as can be obtained, for example, by calciningmagnesium carbonate. Use of this method is only economically expedientat those points where the Bayer liquor itself is produced, sinceotherwise in this case relatively large amounts of water would also haveto be transported.

DE-A-15 92 126 (Kyowa Chemical Ind.) describes the production ofhydrotalcites from various starting materials, for example from asuspension of solid aluminum hydroxide, solid magnesium hydroxide andsodium hydrogen carbonate. The reactions are carried out batchwise hereand the products are separated off from the water phase by filtration orcentrifugation and washed before they are dried.

According to DE-C-44 25 266 (Metallgesellschaft AG), the outlines of thetopic of stabilizing halogenated plastics which is known to thoseskilled in the art are as follows: halogenated thermoplastic resins suchas polyvinyl chloride (PVC) are converted during processing—in thecourse of melt forming—into polyene structures, hydrogen chloride (HCl)being eliminated. The polymer becomes discolored. To improve the thermalstability it is customary to incorporate metal carboxylates (“metalsoaps”) as stabilizers into the resin. However, since the incorporationof substances of this type as sole stabilizers can lead in the case ofrelatively long-duration melt forming to so-called metal burning, whichcauses black discoloration of the polymer, it is general practice to adda costabilizer. Customary costabilizers are, for instance, polyols,organic phosphorous esters or epoxy compounds. According to the teachingof DE-C-44 25 266, specific lithium-containing layer lattice compoundsmay be used to stabilize, in particular, PVC. The use of similarLi-containing layer lattice compounds to stabilize halogenated plasticsis also taught, furthermore, by DE-A-44 25 275 (Metallgesellschaft AG).

DE-A-196 17 138 (Henkel KGaA) discloses a method for producing cationiclayer compounds and the use of these compounds as stabilizers forhalogenated plastics. The compounds are produced by subjecting layercompounds of specific structure to an alkali-induced aging in an aqueousenvironment, the alkali metal hydroxide content of the aqueous mediumbeing set in the range from 1 to 6 molar, the aging temperature in therange from 60 to 100° C. and the aging time in the range from 2.5 to 50hours. Special retreatment methods for further improving the stabilizingaction with respect to halogenated plastics are, however, neitherdisclosed nor suggested in DE-A-196 17 138.

BRIEF SUMMARY OF THE INVENTION

The present invention includes methods of preparing cationic layercompounds, and more particularly, methods wherein a modified cationiclayer compound, according to general formula (I) disclosed herein, isfirst subjected to a crystallization step, and then, a retreatment step.The retreatment in accordance with the present invention comprises steamdrying. The present invention also includes modified cationic layercompounds prepared according to such methods, and methods of stabilizinghalogenated plastics therewith.

The object of the present invention was to provide stabilizers forhalogenated plastics. These stabilizers should be distinguished by animproved activity profile compared with the known prior art. Inparticular, halogenated plastics with these stabilizers incorporatedtherein should have improved values in the range of the initial colorunder thermal stress. The stabilizers, in addition, should have thefollowing properties: good compatibility with calcium compounds and/orzinc compounds; dispersibility in halogenated plastics without impairingtheir rheological properties; high ability to trap well thedecomposition products of halogenated plastics; this means in particularimproved properties with respect to the ability to absorb hydrogenchloride; good long-term stability of halogenated plastics, inparticular PVC (polyvinyl chloride), with the stabilizers incorporatedtherein.

The present invention firstly relates to a method for producing cationiclayer compounds, in which layer compounds of the general formula (I)

[E_(e)Z_(z)D_(d)V_(v)(OH⁻)_(x)](A^(n−))_(a).qH₂O  (I)

where:

E is a monovalent cation selected from the group consisting of thealkali metals,

e is a number in the range from 0 to 2,

Z is a divalent metal cation,

z is a number in the range from 0 to 6,

D is a trivalent metal cation,

d is a number in the range from 0 to 3,

V is a tetravalent metal cation,

v is a number in the range from 0 to 1,

(A^(n−)) is an acid anion of charge n−, where n is an integer from 1 to3, and

q is a number in the range from 1 to 10,

with the proviso that x>a and e+2z+3d+4v=x+na,

(i) are firstly subjected to a crystallization and the resultantmaterial

(ii) is then retreated,

which comprises, for the retreatment, carrying out a steam drying attemperatures in the range from 200 to 260° C. and the duration of theretreatment being in the range from 3 to 6 hours, with the proviso thatsteam, which is applied either directly or in the form of asteam-containing inert carrier gas, is passed continuously over thematerial to be dried at a rate which is in the range from 0.001 to 10mol of water per hour and kilogram of the crystalline layer latticecompound obtained in stage (i).

An inert carrier gas is taken to mean a gas or gas mixture which, underthe retreatment conditions—that is to say temperatures in the range from200 to 260° C. and a retreatment time of from 3 to 6 hours—does notreact with the layer lattice compounds used. The nature of the carriergas is subject to no such restrictions. In practice, in particular airor nitrogen are suitable.

In an embodiment of the present invention, the steam drying is subjectto the proviso that steam, which is applied either directly or in theform of a steam-containing inert carrier gas, is fed at a rate which isin the range from 0.1 to 5 mol of water per hour and kilogram of thecrystalline layer lattice compound obtained in stage (i).

In a preferred embodiment, for the retreatment, a steam-containing inertcarrier gas is applied, with the proviso that the rate of the steampresent in the carrier gas is set in the range from 0.5 to 1.5 mol ofwater per hour and kilogram of the crystalline layer lattice compoundobtained in stage (i) and the rate of the steam-containing carrier gasis set to a value in the range from 500 to 1500 liters—the volumes arebased on a temperature of 20° C. and a pressure of 1 bar—per hour andkilogram of the crystalline layer lattice compound obtained in stage(i).

This procedure may be carried out, for example, by passing an air streamat standard temperature—which is taken to mean here temperatures in therange from 0 to 50° C.—through a storage vessel containing water inorder to enrich the air stream with water vapor in this manner. Thewater-vapor-containing air produced in this manner is then passedcontinuously over the material to be dried, that is to say thecrystalline layer lattice compound obtained in stage (i).

Generally, it is of particular advantage if the material to be dried isspread out in as large an area as possible in a flat layer—for examplein dishes or baths—in order to ensure an intimate contact with the steamor the steam-containing carrier gas. The material to be dried can, ifdesired, be agitated in a mixing manner in the course of this.

A particular advantage of the method of the invention is that it iscarried out at atmospheric pressure in open systems. This isparticularly economic, especially from engineering aspects.

In a further embodiment, the crystallization stage (i) is carried out insuch a manner that the layer compounds (I) are subjected in an aqueousenvironment to an alkali-induced aging, the alkali metal hydroxidecontent of the aqueous medium being set in the range from 1 to 6 molar,the crystallization temperature in the range from 60 to 100° C. and thecrystallization time in the range from 2.5 to 50 hours. For details ofthe crystallization step specified here, reference is made to DE-A-19617 138 of the applicant. At this point, reference may be made only tothe essential parameters:

The aging medium of the crystallization stage (i) is a from 1 to 6 molaraqueous alkali metal hydroxide solution. However, preferably, from 3 to5 molar solutions are employed. The type of alkali metal hydroxide whichis used to provide the aqueous-alkaline environment is not critical perse. Generally, however, sodium hydroxide is used.

The following applies with respect to the temperature of thecrystallization stage (i): A temperature in the range from 60 to 100° C.is set. Preference is given here to a range from 70 to 90° C.

With respect to the time required for the crystallization stage (i), thefollowing applies: In principle, a range from 2.5 to 50 hours isemployed. If the time falls below the specified lower limit, thesought-after improvement in the properties of the layer compounds is notensured. If the specified upper limit is exceeded, further improvementin the properties occurs only to a very restricted extent and it istherefore uneconomic. Preferably, crystallization times in the range offrom 5 to 15 hours are employed.

In one embodiment, to carry out the method of the invention, layercompounds of the general formula (I) are used in which v is zero. Theselayer compounds may therefore be described by the general formula (I*):

[E_(e)Z_(z)D_(d)(OH⁻)_(x)](A^(n−))_(a).qH₂O  (I*)

where:

E is a monovalent cation selected from the group consisting of thealkali metals,

e is a number in the range from 0 to 2,

Z is a divalent metal cation,

z is a number in the range from 0 to 6,

D is a trivalent metal cation,

d is a number in the range from 0 to 3,

(A^(n−)) is an acid anion of the charge n−, where n is an integer from 1to 3, and

q is a number in the range from 1 to 10,

with the proviso that x>a and e+2z+3d=x+na.

In a further embodiment, to carry out the process of the invention,layer compounds of the general formula (I) are used in which e is zero.These layer compounds may therefore be described by the general formula(I**):

 [Z_(z)D_(d)V_(v)(OH⁻)_(x)](A^(n−))_(a).qH₂O  (I**)

where:

Z is a divalent metal cation,

z is a number in the range from 0 to 6,

D is a trivalent metal cation,

d is a number in the range from 0 to 3,

V is a tetravalent metal cation,

v is a number in the range from 0 to 1,

(A^(n−)) is an acid anion of charge n−, where n is an integer from 1 to3, and

q is a number in the range from 1 to 10,

with the proviso that x>a and 2z+3d+4v=x+na.

In a preferred embodiment, to carry out the process of the inventionlayer compounds of the general formula (I) are used in which e and v areeach zero. These layer compounds may therefore be described by thegeneral formula (I***):

[Z_(z)D_(d)(OH⁻)_(x)](A^(n−))_(a).qH₂O  (I***)

where:

Z is a divalent metal cation,

z is a number in the range from 0 to 6,

D is a trivalent metal cation,

d is a number in the range from 0 to 3,

(A^(n−)) is an acid anion of charge n−, where n is an integer from 1 to3, and

q is a number in the range from 1 to 10,

with the proviso that x>a and 2z+3d=x+na.

The layer compounds according to formula (I***) are the “classic”hydrotalcites which have long been known to those skilled in the art. Ofthese compounds, in turn, preference to given to those in which D isaluminum, d is the number 1 and z is a number in the range from 1 to 5.These specific hydrotalcites are characterized by the general formula(I****):

[Z_(z)Al(OH⁻)_(x)](A^(n−))_(a).qH₂O  (I****)

where:

Z is a divalent metal cation,

z is a number in the range from 1 to 5,

(A^(n−)) is an acid anion of charge n−, where n is an integer from 1 to3, and

q is a number in the range from 1 to 10,

with the proviso that x>a and 2z+3=x+na.

The essence of the present invention is that the lattice structure ofany cationic layer compounds (I)—in particular classic hydrotalcites ofthe general formula (I***) and (I****)—experiences, in the course of theretreatment, a modification in a manner such that—due to the extent ofcrystallinity which is optimized as a result—the effect of the resultantlayer compounds as co-stabilizer for halogenated plastics is permanentlyimproved. It is not critical here which origin the layer compound (I)used has. It can either be of natural origin or can be synthesized.

The change in crystallinity of the cationic layer compounds can bedetected by X-ray structural analysis. It is proved here thatsynthetically produced layer compounds (I) which are used as startingmaterial in the process according to the invention have relatively broadreflections in the X-ray structure diagram. After carrying out the firstpartial step of the process according to the invention, that is to saythe crystallization stage (i), the reflections are sharp and narrow,which indicates high crystallinity. After carrying out the secondpartial stage of the process according to the invention, that is to saythe retreatment stage (ii), the reflections are again slightlybroadened, from which a slightly decreased crystallinity in comparisonwith the layer lattice compound obtained in stage (i) may be concluded.As the performance tests indicate, when the compounds prepared accordingto the invention are used in halogenated plastics, an improvedstabilizing action against thermal or photochemical degradation results.

DETAILED DESCRIPTION OF THE INVENTION

The cationic layer compounds (I) are compounds which are known per sewhose structure and production have been described, for example, by W.T. Reichle in Chemtec (January 1986), pages 58-63.

The prototype of cationic layer compounds is the mineral hydrotalcite[Mg₆Al₂(OH)₁₆](CO₃).4H₂O. Hydrotalcite is derived structurally frombrucite [Mg(OH)₂]. Brucite crystallizes in a layer structure containingthe metal ions in octahedral interstices between two layers ofhexagonally tightly packed (OH⁻) ions. Only every second layer ofoctahedral interstices is occupied by metal ions M, so that layerpackages (OH)—M—(OH) are formed. The intermediate layers are empty inbrucite; in hydrotalcite, some—roughly every second to fifth—of theMg(II) ions are replaced at random by Al(III) ions. The layer package asa result becomes positively charged overall. This charge is balanced byanions which are situated in the intermediate layers together withreadily removable water of crystallization. Diagram 1shows—schematically—the layer structure of hydrotalcite.

Hydrotalcites form pulverulent masses with a talc-like feel having BETsurface areas of up to about 150 m²/g. Two basic syntheses are disclosedin the literature: one possible synthesis is to treat aqueous solutionsof the corresponding metal salts with alkali metal hydroxide solution,the resulting hydrotalcite precipitating out. Another method starts fromwater-insoluble initial compounds such as metal oxides and metalhydroxides. These syntheses are heterogeneous reactions which arecustomarily carried out in the autoclave.

Diagram 1

Structure of Hydrotalcite

As mentioned above, hydrotalcite is merely the prototype of catoniclayer compounds. However, the synthetic methods known from hydrotalciteare also used as a basis in general for synthesizing any cationic layercompounds. As known to those skilled in the art, these synthetic methodsmay be classified quite in general as hydrothermal synthesis.Hydrothermal synthesis in the narrower sense is taken to mean thesynthesis of minerals from aqueous suspensions which have been heated tohigh temperatures—above a temperature of 100° C. and a pressure of 1atm; hydrothermal syntheses are generally carried out in pressurevessels, since the temperatures employed are far above the boilingtemperature of water, generally even above its critical temperature (cf.Römpps Chemie-Lexikon [Römpps's Chemistry Lexicon], ⁷1973, p. 1539).

For the purposes of the invention, the cationic layer compounds (I) arepreferred where Z is at least one divalent metal ion selected from thegroup consisting of magnesium, calcium and zinc. Preferably, Z isprecisely one divalent metal ion from said group and in particularmagnesium. Cationic layer compounds of the general formula I are veryparticularly preferred, where A^(n−) is an acid anion having the charge(n−) selected from the anion group consisting of carbonate,hydrogencarbonate, perchlorate, acetate, nitrate, tartrate, oxalate andiodide, preferably carbonate. If in the commentary on the above formulaI mention is made of at least one divalent metal ion, this means that inthe cationic layer compound different divalent metal ions can be presentadjacently. The indices x, y and z, and also m, can be integers ornonintegral numbers within the specified conditions. Particularlyadvantageously, in cationic layer compounds of the general formula I, Zis magnesium and A^(n−) is carbonate.

The BET surface area of the cationic layer compounds (I) to be usedaccording to the invention is not critical per se. However, preferably,layer compounds (I) are used whose BET surface area is greater than 50m²/g. In a preferred embodiment of the present invention, layercompounds (I) are used which have a mean particle size in the range from20 to 50 μm.

Examples of suitable cationic layer compounds are synthetichydrotalcites which are also called basic aluminum magnesium carbonatesand which can be produced in general by the method described in GermanPublished Application DE-B-15 92 126 and in the German Laid-OpenApplications DE-A-20 61 114 or DE-A-29 05 256.

Suitable sources of divalent metal ions are their carbonates, carbonatehydroxides, hydroxides, oxides or their water-soluble salts, for examplethe nitrates, chlorides, sulfates or perchlorates. Particularlypreferably, sources of divalent metal ions are selected that alreadycontain the A^(n−) anion. In this case, it is not necessary to add anadditional source of these anions. For example, it is particularlypreferred to use at least a part of the divalent metal ions ascarbonates or as carbonate hydroxides. If the sole source of divalentmetal ions used is their oxides or hydroxides, it is necessary to add anadditional source of the anions A^(n−), for example in the form ofalkali metal salts. Alkali metal salts of carbonic acid and/or of oxoacids of halogens, for example perchloric acid, are preferred, which canbe added in amounts of from 1 to 100 mol % based on the aluminum contentof the reaction mixture. For example, sodium carbonate can be added tothe reaction batch.

The source of aluminum used can be not only finely particulate, activealuminum(III) hydroxide combined with sodium hydroxide, but also NaAlO₂.In addition aluminum chloride, aluminum bromide, aluminum nitrate andaluminum sulfate.

The present invention also relates to cationic layer compounds which areobtainable by firstly subjecting layer compounds of the general formula(I)

[E_(e)Z_(z)D_(d)V_(v)(OH⁻)_(x)](A^(n−))_(a).qH₂O  (I)

where:

E is a monovalent cation selected from the group consisting of thealkali metals,

e is a number in the range from 0 to 2,

Z is a divalent metal cation,

z is a number in the range from 0 to 6,

D is a trivalent metal cation,

d is a number in the range from 0 to 3,

V is a tetravalent metal cation,

v is a number in the range from 0 to 1,

(A^(n−)) is an acid anion of charge n−, where n is an integer from 1 to3, and

q is a number in the range from 1 to 10,

with the proviso that x>a and e+2z+3d+4v=x+na,

(i) to a crystallization and

(ii) then retreating the resultant material,

which comprises, for the retreatment, carrying out a steam drying attemperatures in the range from 200 to 260° C. and the duration of theretreatment being in the range from 3 to 6 hours, with the proviso thatsteam, which is applied either directly or in the form of asteam-containing inert carrier gas, is passed continuously over thematerial to be dried at a rate which is in the range from 0.001 to 10mol of water per hour and kilogram of the crystalline layer latticecompound obtained in stage (i).

The present invention further relates to compositions for stabilizinghalogenated plastics from thermal degradation or photochemicaldegradation, which compositions comprise cationic layer compounds whichare obtainable by firstly subjecting layer compounds of the generalformula (I)

[E_(e)Z_(z)D_(d)V_(v)(OH⁻)_(x)](A^(n−))_(a).qH₂O  (I)

where:

E is a monovalent cation selected from the group consisting of thealkali metals,

e is a number in the range from 0 to 2,

Z is a divalent metal cation,

z is a number in the range from 0 to 6,

D is a trivalent metal cation,

d is a number in the range from 0 to 3,

V is a tetravalent metal cation,

v is a number in the range from 0 to 1,

(A^(n−)) is an acid anion of charge n−, where n is an integer from 1 to3, and

q is a number in the range from 1 to 10,

with the proviso that x>a and e+2z+3d+4v=x+na,

(i) to a crystallization and

(ii) then retreating the resultant material,

which comprises, for the retreatment, carrying out a steam drying attemperatures in the range from 200 to 260° C. and the duration of theretreatment being in the range from 3 to 6 hours, with the proviso thatsteam, which is applied either directly or in the form of asteam-containing inert carrier gas, is passed continuously over thematerial to be dried at a rate which is in the range from 0.001 to 10mol of water per hour and kilogram of the crystalline layer latticecompound obtained in stage (i).

The substances produced according to the invention can be usedadvantageously as stabilizers for halogenated thermoplasticcompositions. Examples of such resins are PVC, polyvinylidene chloride,chlorinated or chloro-sulfonated polyethylene, chlorinated polypropyleneor chlorinated ethylene/vinyl acetate copolymers. The cationic layerlattice compounds produced according to the invention are particularlysuitable as stabilizers for resins of the PVC type, these being taken tomean firstly vinyl chloride homopolymers, and secondly copolymers ofvinyl chloride with other monomers.

The present invention further relates accordingly to the use of cationiclayer compounds which are obtainable by firstly subjecting layercompounds of the general formula (I)

[E_(e)Z_(z)D_(d)V_(v)(OH⁻)_(x)](A^(n−))_(a).qH₂O  (I)

where:

E is a monovalent cation selected from the group consisting of thealkali metals,

e is a number in the range from 0 to 2,

Z is a divalent metal cation,

z is a number in the range from 0 to 6,

D is a trivalent metal cation,

d is a number in the range from 0 to 3,

V is a tetravalent metal cation,

v is a number in the range from 0 to 1,

(A^(n−)) is an acid anion of charge n−, where n is an integer from 1 to3, and

q is a number in the range from 1 to 10,

with the proviso that x>a and e+2z+3d+4v=x+na,

(i) to a crystallization and

(ii) then retreating the resultant material,

which comprises, for the retreatment, carrying out a steam drying attemperatures in the range from 200 to 260° C. and the duration of theretreatment being in the range from 3 to 6 hours, with the proviso thatsteam, which is applied either directly or in the form of asteam-containing inert carrier gas, is passed continuously over thematerial to be dried at a rate which is in the range from 0.001 to 10mol of water per hour and kilogram of the crystalline layer latticecompound obtained in stage (i), for stabilizing halogenated plasticsfrom thermal degradation or photochemical degradation.

Preference is given here to the use of the cationic layer compoundsproduced according to the invention as co-stabilizers for halogenatedplastics stabilized with calcium salts and/or zinc salts of carboxylicacids having from 6 to 22 carbons. In particular, the cationic layercompounds produced according to the invention are used as co-stabilizersin polyvinyl chloride. For this the cationic layer compounds—withouttaking into account the content of any organic additives present—areadded in amounts of from 0.01 to 5, preferably from 0.1 to 3, parts byweight—based on 100 parts by weight of synthetic resins. Generally, theyare mechanically mixed with the plastics present in granular form,before the shaping is carried out, for example in the calender andextrusion processes. Generally, the commercial zinc salts and/or calciumsalts of carboxylic acids having from 6 to 22 carbons are added asconventional stabilizers simultaneously with the cationic layercompounds. Obviously, other conventional additives, such as the heatstabilizers described in European Application EP-A-189 899, can also beused. The amounts of the stabilizers and co-stabilizers can be varied inany proportion with the proviso that the total stabilizer addition iswithin the quantitative limit of from 0.5 to 5 parts by weight—based on100 parts by weight of synthetic resins. The minimum amount of cationiclayer compound is therefore at least 0.01% by weight.

The use of the cationic layer compounds of the invention improves theaction of zinc soaps and/or calcium soaps in the stabilization of thehalogenated plastics. In addition, the cationic layer compounds of theinvention can be incorporated outstandingly as co-stabilizers into thehalogenated plastics without adversely affecting the rheology of theplastics.

If desired, the cationic layer compounds produced according to theinvention can then be modified with at least one liquid or low-melting,dispersing additive selected from compounds of the following listedgroups A) to F) by intensive mixing at room temperature (15 to 25° C.)or a temperature below the decomposition temperatures of the cationiclayer compounds and/or the additives, preferably below 300° C. Thegroups A) to F) are:

A) Polyols having from 3 to 30 carbons and at least 2 hydroxyl groups.

B) Esters of partially or completely epoxidized unsaturated carboxylicacids having from 6 to 22 carbons.

C) Complete and partial esters of polyols having from 3 to 30 carbonsand from 2 to 12 hydroxyl groups with carboxylic acids having from 6 to22 carbons.

D) Alkyl phosphites and aryl phosphites.

E) Anions of saturated or unsaturated fatty acids having from 6 to 22carbons.

F) Polymers soluble in water at pHs above 8 having a molecular weight offrom 500 to 50,000.

Suitable additives of group A) are polyols having at least two hydroxylgroups and a total of from 3 to 30 carbons. Examples of such polyols arediols having from 3 to 30 carbons, such as butanediols, hexanediols,dodecanediols and polyols such as trimethylolpropane, pentaerythritol,glycerol and their industrial oligomer mixtures having mean degrees ofcondensation of from 2 to 10. Very particular preference is given topolyols having from 3 to 30 carbons whose C skeleton bears, at adistance of 3 carbons, at least one hydroxyl group or one ether oxygen,preferably glycerol and/or the industrial oligoglycerol mixtures havingmean degrees of condensation of from 2 to 10. In particular, alsosuitable for this is tris(2-hydroxyethyl)isocyanurate, known as “THEIC”(EP-B-377 428).

The additives of group B) are esters of partially or completelyepoxidized unsaturated carboxylic acids having from 6 to 22 carbons.Suitable esters are esters of monohydric, dihydric and/or trihydricalcohols which are completely esterified with epoxidized unsaturatedcarboxylic acids having from 6 to 22 carbons, such as methyl,2-ethylhexyl, ethylene glycol, butanediol, neopentyl glycol, glyceroland/or trimethylolpropane esters of epoxidized lauroleic acid,palmitoleic acid, oleic acid, ricinoleic acid, linoleic acid and/orlinolenic acid. Preference is given to esters of trihydric alcohols andcompletely epoxidized unsaturated carboxylic acids having from 12 to 22carbons, and in particular esters of glycerol with completely epoxidizedunsaturated carboxylic acids having from 12 to 22 carbons. Thecarboxylic acid component can be derived, for example, from palmitoleicacid, oleic acid, elaidic acid, petroselinic acid, ricinoleic acid,linolenic acid, gadoleic acid or erucic acid. The unsaturated carboxylicacids are epoxidized by known methods. As customary in fat chemistry,the glycerides of epoxidized carboxylic acids can also be industrialmixtures as obtained by epoxidation of natural unsaturated fats andoils. Preferably, epoxidized rapeseed oil, epoxidized unsaturatedsoybean oil and/or epoxidized sunflower seed oil from recent cultivationare used.

The additives of group C) are complete or partial esters which areobtained by the relevant methods of preparative organic chemistry, forexample by acid-catalyzed reaction of polyols with carboxylic acids.Suitable polyol components here are those which have already beendescribed in group A). As acid component, preference is given toaliphatic, saturated and/or unsaturated carboxylic acids having from 6to 22 carbons, such as caproic acid, caprylic acid, capric acid, lauricacid, myristic acid, palmitic acid, palmitoleic acid, stearic acid,oleic acid, ricinoleic acid, linoleic acid, linolenic acid, behenic acidor erucic acid. As customary in fat chemistry, the carboxylic acidcomponent can also be an industrial mixture as produced in the pressurecleavage of natural fats and oils. Preference is given to partial estersof glycerol and in particular of its industrial oligoglycerol mixtureshaving mean degrees of condensation of from 2 to 10 and saturated and/orunsaturated aliphatic carboxylic acids having from 6 to 22 carbons.

The additives of group D) used can be alkyl phosphites and arylphosphites, preferably those of the general formula II

where R¹, R² and R³ independently of one another are an alkyl radicalhaving from 1 to 18 carbons or a phenyl radical. Typical examples ofadditives of group D) are tributyl phosphite, triphenyl phosphite,dimethyl phenyl phosphite and/or dimethyl stearyl phosphite. Preferenceis given to diphenyl decyl phosphite.

Suitable additives of group E) are anions of saturated ormonounsaturated or polyunsaturated fatty acids having from 6 to 22carbons, which can be unbranched or branched. Owing to their readieravailability, preference is given to unbranched fatty acids. Pure fattyacids are suitable here, for example lauric acid, myristic acid,palmitic acid, stearic acid, lauroleic acid, myristoleic acid,palmitoleic acid, oleic acid, linoleic acid or linolenic acid. It isalso economically attractive to use fatty acid mixtures, as areobtainable from the cleavage of natural oils and fats. It is notimportant here whether the fatty acids are used as such or as—preferablywater-soluble—salts, for example as sodium salts or potassium salts.Since the reaction mixture is strongly alkaline, the reaction productwill in any case contain the fatty acids in the form of their anions.

Additives of group F) are polymers which are soluble in water at pHsabove 8, preferably at pHs of from 9 to 12, and which have a mean(number average) molecular weight of from 500 to 50,000. The term“soluble” means in this context that the polymeric additives arecompletely dissolved at more than 0.01% by weight in an aqueous solutionof pH 10, established using alkali metal hydroxides at 20° C.,preferably at at least 0.1% by weight and in particular under thespecified conditions. In principle, as polymeric additives, all polymerscan be used which are known to those skilled in the art as pigmentdispersers (cf. Kirk-Othmer “Encyclopedia of Chemical Technology”, Vol.7, third edition, 1979, pages 840-841 or Ullmann's “Encyclopedia ofIndustrial Chemistry”, Vol. A8, 5th edition, 1987, pages 586-601),provided that they comply with the preconditions of solubility andmolecular weight. Preference is given as polymeric additives to acrylicacid homopolymers and copolymers and methacrylic acid homopolymers andcopolymers, ligninsulfonates and trimeric fatty acids. Those which aresuitable in particular are polymeric additives selected from the groupconsisting of polymers of acrylic acid and methacrylic acid and theircopolymers with unsaturated monomers containing sulfonic acid groups,unsaturated monomers containing phosphonic acid groups, unsaturatedaliphatic carboxylic acids having from 3 to 5 carbons, amides ofunsaturated aliphatic carboxylic acids having from 3 to 5 carbons,amino-containing unsaturated monomers and/or their salts, vinyl acetate,vinyl chloride, acrylonitrile, vinylidene chloride, 1,3-butadiene,styrene, alkylstyrenes having from 1 to 4 carbons in the alkyl radical.Examples of these are polyacrylic acid, polymethacrylic acid—hereinafteracrylic acid and methacrylic acid and their derivatives will beabbreviated as (meth)acrylic acid and derivatives for simplicity—and/ortheir salts such as polysodium(meth)acrylate, copolymers of(meth)acrylic acid with maleic acid, maleic anhydride, styrenesulfonicacid, μ-methylstyrene, 2-vinylpyridine, 1-vinylimidazole,dimethylaminopropyl(meth)acrylamide,2-(meth)acrylamido-2-methylpropanesulfonic acid, (meth)acrylamide,N-hydroxydimethyl(meth)acrylamide and/or their salts. Very particularpreference among the polymeric additives is given to those which havepredominantly anionic character, that is to say which bear the majorityof acid groups free or in the form of their salts. In particular,preference is given to polymers of (meth)acrylic acid and its copolymerswith styrene, alkylstyrenes having from 1 to 4 carbons in the alkylradical, styrenesulfonic acid, maleic acid and/or salts thereof, inparticular sodium salts thereof and maleic anhydride. Expediently, thepolymeric additives have a molecular weight of from 1000 to 10,000. Thepolymeric additives can be produced by known processes such assolvent-free polymerization or solvent polymerization (cf. Ullmann'sEncyclopädie der technischen Chemie [Encyclopedia of IndustrialChemistry], Volume 19, 4th edition, pages 2-11, 1980). Methods forproducing ligninsulfonic acid and its salts are also described inUllmann's Encyclopadie der technischen Chemie, Volume 16, 4th edition,pages 254-257, 1978. Trimeric fatty acids are commercial products whichare produced as residue in the distillation of dimeric fatty acids, suchas Pripol® 1040 from Unichema or Emery® 1000 from Emery.

The term low-melting additives of groups A) to F) is taken to meanadditives which can be converted into the liquid state at atmosphericpressure below the abovementioned decomposition temperatures. Instead ofthe intensive mixing, if desired, the cationic layer compounds obtainedafter the production can then be ground with one or more additivesselected from the groups A) to F) in the presence of polar organicsolvents or water, preferably using grinding-medium mills and inparticular a ball mill, dried and if appropriate redried. The term polarorganic solvents is taken to mean hydrocarbon compounds which are liquidat room temperature (from 15 to 25° C.) which have at least onesubstituent which is more electronegative than carbon. These includechlorinated hydrocarbons, alcohols, ketones, esters, ethers and/orglycol ethers. Suitable polar organic solvents are methanol, ethanol,n-butanol, acetone, methyl ethyl ketone, methyl isobutyl ketone,cyclohexanol, isophorone, ethyl acetate, ethyl lactate, 2-methoxyethylacetate, tetrahydrofuran, ethyl glycol monomethyl ether, diethyleneglycol monoethyl ether. For this modification with the organic additivesto be carried out retrospectively, i.e. after drying the cationic layercompounds produced according to the invention to form a powder, suitableamounts of additive are between about 5 and about 100% by weight, basedon the cationic layer compound.

The use of the additives A) to F) in combination with cationic layercompounds is moreover disclosed by the publications WO 92/06135, WO92/20732 and WO 92/20619.

The cationic layer lattice compounds produced according to the inventioncan be used as sole stabilizers for halogenated thermoplastic resins.However, preferably, they are used in combination with otherstabilizers. In addition to the abovementioned use in combination withmetal soaps, here, primarily, 1,3-diketone compounds, organic esters ofphosphorous acid, polyols and amino acids are taken into consideration.

Examples of 1,3-diketone compounds are: dibenzoyl methane,stearoylbenzoylmethane, palmitoylbenzoylmethane,myristoylbenzoylmethane, lauroylbenzoylmethane, benzoylacetone,acetylacetone, tribenzoylmethane, diacetylacetobenzene, p-methoxy- andstearoylacetophenone, ethyl acetoacetate.

Examples of suitable esters of phosphorous acid are triaryl phosphites,such as triphenyl phosphite, tris(p-nonylphenyl) phosphite (TNPP); alkylaryl phosphites such as monoalkyl diphenyl phosphites, for examplediphenyl isooctyl phosphite, diphenyl isodecyl phosphite and dialkylmonophenyl phosphites, such as phenyl diisooctyl phosphite, phenyldiisodecyl phosphite and trialkyl phosphites, such as triisooctylphosphite and tristearyl phosphite.

Examples of suitable polyols are trimethylolpropane,di-(trimethylolpropane), erythritol, pentaerythritol, dipentaerythritol,sorbitol, mannitol.

Examples of amino acid derivatives are glycine, alanine, lysine,tryptophan, acetylmethionine, pyrrolidonecarboxylic acid,beta-aminocrotonic acid, alpha-aminoacrylic acid, alpha-aminoadipic acidand esters derived therefrom. The alcohol components of these estersinclude monohydric alcohols such as methanol, ethanol, propanol,isopropanol, butanol, 2-ethylhexanol, octanol, isooctanol, laurylalcohol, stearyl alcohol, and polyols such as ethylene glycol, propyleneglycol, 1,3-butanediol, 1,4-butanediol, glycerol, diglycerol,trimethylolpropane, pentaerythritol, dipentaerythritol, sorbitol andmannitol.

Examples of suitable epoxy compounds are epoxidated soybean oil,epoxidated rapeseed oil, epoxidated esters of unsaturated fatty acidssuch as epoxidated methyl oleate, epoxidated butyl oleate, epoxidatedalicyclic substances, glycidyl ethers such as bisphenol-A diglycidylether, bisphenol-F diglycidyl ether, in addition glycidyl esters such asglycidyl acrylate and glycidyl methacrylate.

The examples hereinafter serve to illustrate the invention and are notto be understood as restrictive.

EXAMPLES A) Production Example 1

In-situ production of the layer compound (I)

60 g of Al(OH)₃ moist hydrate (equivalent to 66% of Al₂O₃) weredissolved in 75 g of a 50% strength by weight aqueous sodium hydroxidesolution at a temperature of 80° C. 27.4 g of soda were then added withstirring. To the resultant suspension was added slowly dropwise asolution of 130 g of magnesium chloride in 75 g of deionized water.

Crystallization step (i)

The reaction mixture was heated to 80° C., admixed with 152.6 g of a 50%strength by weight aqueous sodium hydroxide solution and crystallizedfor eight hours. The resultant product was filtered and washed twice,each time with 500 ml of water. The yield was 60 g of crystallineproduct.

Retreatment step (ii)

The resultant crystalline product was then subjected to a retreatment.For this purpose, the crystalline product was spread in a ceramic dish(diameter about 15 cm, layer height about 0.5 cm), this ceramic dish wasplaced in a muffle furnace heated to 240° C. and steam-containing airwas continuously passed over the material to be dried for a period of 5hours. The steam-containing air was produced as follows: at 20° C., roomair of a relative humidity of 65% was passed through a wash bottle whichcontained 1 liter of water at a temperature of 20° C. at a flow rate of80 l/h (liters per hour). The air stream which was enriched with watervapor in this manner was then continuously passed over the material tobe dried in the muffle furnace for a period of 3 hours.

Example 2

Example 1 was repeated, but in the retreatment step (ii), thesteam-enriched air stream was passed over the material to be dried inthe muffle furnace for a period of 4 hours.

Example 3

Example 1 was repeated, but in the retreatment step (ii), thesteam-enriched air stream was passed over the material to be dried inthe muffle furnace for a period of 5 hours.

Example 4

Example 1 was repeated, but in the retreatment step (ii), thesteam-enriched air stream was passed over the material to be dried inthe muffle furnace for a period of 6 hours.

Comparison Example 1

Example 1 was repeated, but in the retreatment step (ii), thesteam-enriched air stream was passed over the material to be dried inthe muffle furnace for a period of 1 hour.

Comparison Example 2

Example 1 was repeated, but in the retreatment step (ii), thesteam-enriched air stream was passed over the material to be dried inthe muffle furnace for a period of 8 hours.

B) Performance tests

The substances produced according to the abovementioned examples andcomparison examples were examined for their ability to improve the colorstability of PVC. For this purpose, use was made of the parametersexplained below “initial color” and “long-term stability”. The testspecimens used were milled sheets from which test strips were stampedout. The milled sheets were produced using the following testformulation as a basis:

PVC (Solvic 268; Solvay) 100.0 parts Calcium stearate 0.5 part Zincstearate 0.5 part Rhodiastab 50 (Rhône-Poulenc) 0.2 part Testsubstance^(a)) 1.0 part ^(a))Test substance = the substances producedaccording to the abovementioned examples and comparison examples.

The test specimens were produced by homogenizing and plasticizing thehard PVC composition and said additives on a laboratory roll mill for 5minutes at 170° C. From the roughly 0.5 mm thick milled sheets thusproduced, test strips 15 mm wide were cut out.

Immediately after the milled sheets were produced, their color, theso-called initial color, was determined. For this purpose, the L*,a*,b*method (cf. DIN 6174, CIELAB 1976) known to those skilled in the art wasused. The b* value indicates the position on the blue/yellow axis.Customarily the b* value is also called yellow value. For themeasurements, a commercial instrument called “Micro Color” (Dr. Lange)was used. The initial colors are summarized in Table 1. It was foundthat the milled sheets having a content of the test substances accordingto the invention (produced according to Examples 1 to 4) hadsignificantly better initial colors than the milled sheets having acontent of the test substances which were not according to the invention(produced according to Comparison Examples 1 and 2).

As a further parameter, the time taken until the test strips becamediscolored black during a temperature treatment in a thermal furnace wasdetermined (see DIN 5033). For this purpose thetest-substance-containing test strips were heated at 180° C. in athermal furnace, in which case the test strips were removed briefly fromthe furnace for visual inspection at intervals of 15 minutes. The timein minutes until black discoloration is termed long-term stability. Thetest results are summarized in Table 1.

TABLE 1 Retreatment Test substance time in step Long-term according to(ii) Initial color^(b)) stability^(c)) Comparison 1 hour 17.1 105example 1 Example 1 3 hours 15.6 105 Example 2 4 hours 14.8 105 Example3 5 hours 14.6 105 Example 4 6 hours 15.3 105 Comparison 8 hours 17.8 60Example 2 ^(b))Initial color = yellow value b* ^(c))Long-term stability= minutes until black discoloration

What is claimed is:
 1. A method of preparing a modified cationic layercompound, said method comprising: (a) providing a layer compound of thegeneral formula (I):[E_(e)Z_(z)D_(d)V_(v)(OH⁻)_(x)](A^(n−))_(a).qH₂O  (I) wherein Erepresents one or more monovalent alkali metal cations, e represents anumber of from 0 to about 2, Z represents one or more divalent metalcations, z represents a number of from 0 to about 6, D represents one ormore trivalent metal cations, d represents a number of from 0 to about3, V represents one or more tetravalent metal cations, v represents anumber of from 0 to about 1, (A^(n−)) represents an acid anion wherein nrepresents an integer of from 1 to 3, q represents a number of fromabout 1 to about 10, and wherein x>a and e+2z+3d+4v=x+na; (b) subjectingthe layer compound to crystallization to provide a resultant material;and (c) subjecting the resultant material to steam drying at atemperature of from about 200° C. to about 260° C. for a period of timeof from about 3 to about 6 hours, said steam drying comprising passing asource of steam continuously over the resultant material at a rate offrom about 0.001 to about 10 moles of water per hour, per kilogram ofthe resultant material.
 2. The method according to claim 1, wherein thesource of steam is passed continuously over the resultant material at arate of from about 0.1 to about 5 moles of water per hour, per kilogramof the resultant material.
 3. The method according to claim 1, whereinsaid steam drying comprises passing a steam-containing inert carrier gascontinuously over the resultant material at a rate of from about 500 toabout 1500 liters, at 20° C. and 1 bar, per hour, per kilogram of theresultant material; and wherein steam is present in the steam-containinginert carrier gas at a rate of from about 0.5 to about 1.5 moles ofwater per hour, per kilogram of the resultant material.
 4. The methodaccording to claim 1, wherein the crystallization comprisesalkali-induced aging in an aqueous medium containing an alkali metalhydroxide at a temperature of from about 60° C. to about 100° C. for atime period of from about 2.5 hours to about 50 hours, and wherein thealkali metal hydroxide is present in a concentration of from about 1molar to about 6 molar.
 5. The method according to claim 2, wherein thecrystallization comprises alkali-induced aging in an aqueous mediumcontaining an alkali metal hydroxide at a temperature of from about 60°C. to about 100° C. for a time period of from about 2.5 hours to about50 hours, and wherein the alkali metal hydroxide is present in aconcentration of from about 1 molar to about 6 molar.
 6. The methodaccording to claim 3, wherein the crystallization comprisesalkali-induced aging in an aqueous medium containing an alkali metalhydroxide at a temperature of from about 60° C. to about 100° C. for atime period of from about 2.5 hours to about 50 hours, and wherein thealkali metal hydroxide is present in a concentration of from about 1molar to about 6 molar.
 7. The method according to claim 1, wherein vequals zero.
 8. The method according to claim 4, wherein V equals zero.9. The method according to claim 1, wherein e equals zero.
 10. Themethod according to claim 4, wherein e equals zero.
 11. The methodaccording to claim 1, wherein v and e both equal zero.
 12. The methodaccording to claim 4, wherein v and e both equal zero.
 13. The methodaccording to claim 11, wherein D represents an aluminum cation, d equals1, and x represents a number of from about 1 to about
 5. 14. The methodaccording to claim 12, wherein D represents an aluminum cation, d equals1, and x represents a number of from about 1 to about
 5. 15. A modifiedcationic layer compound prepared by the method according to claim
 1. 16.A modified cationic layer compound prepared by the method according toclaim
 14. 17. A stabilizer composition for halogen-containing plastics,said composition comprising a modified cationic layer compound preparedby providing a layer compound of the general formula (I):[E_(e)Z_(z)D_(d)V_(v)(OH⁻)_(x)](A^(n−))_(a).qH₂O  (I) wherein Erepresents one or more monovalent alkali metal cations, e represents anumber of from 0 to about 2, Z represents one or more divalent metalcations, z represents a number of from 0 to about 6, D represents one ormore trivalent metal cations, d represents a number of from 0 to about3, V represents one or more tetravalent metal cations, v represents anumber of from 0 to about 1, (A^(n−)) represents an acid anion wherein nrepresents an integer of from 1 to 3, q represents a number of fromabout 1 to about 10, and wherein x>a and e+2z+3d+4v=x+na; subjecting thelayer compound to crystallization to provide a resultant material; andsubjecting the resultant material to steam drying at a temperature offrom about 200° C. to about 260° C. for a period of time of from about 3to about 6 hours, said steam drying comprising passing a source of steamcontinuously over the resultant material at a rate of from about 0.001to about 10 moles of water per hour, per kilogram of the resultantmaterial.
 18. The stabilizer composition according to claim 17, whereinv and e both equal zero, D represents an aluminum cation, d equals 1,and x represents a number of from about 1 to about 5; wherein thecrystallization comprises alkali-induced aging in an aqueous mediumcontaining an alkali metal hydroxide at a temperature of from about 60°C. to about 100° C. for a time period of from about 2.5 hours to about50 hours, and the alkali metal hydroxide is present in a concentrationof from about 1 molar to about 6 molar; and wherein the source of steamis passed continuously over the resultant material at a rate of fromabout 0.1 to about 5 moles of water per hour, per kilogram of theresultant material.
 19. A method of stabilizing a halogen-containingplastic, said method comprising: (a) providing a halogen-containingplastic composition; (b) providing a modified cationic layer compound;and (c) combining the halogen-containing plastic composition and themodified cationic layer compound; wherein the modified cationic layercompound is prepared by providing a layer compound of the generalformula (I): [E_(e)Z_(z)D_(d)V_(v)(OH⁻)_(x)](A^(n−))_(a).qH₂O  (I)wherein E represents one or more monovalent alkali metal cations, erepresents a number of from 0 to about 2, Z represents one or moredivalent metal cations, z represents a number of from 0 to about 6, Drepresents one or more trivalent metal cations, d represents a number offrom 0 to about 3, V represents one or more tetravalent metal cations, vrepresents a number of from 0 to about 1, (A^(n−)) represents an acidanion wherein n represents an integer of from 1 to 3, q represents anumber of from about 1 to about 10, and wherein x>a and e+2z+3d+4v=x+na;subjecting the layer compound to crystallization to provide a resultantmaterial; and subjecting the resultant material to steam drying at atemperature of from about 200° C. to about 260° C. for a period of timeof from about 3 to about 6 hours, said steam drying comprising passing asource of steam continuously over the resultant material at a rate offrom about 0.001 to about 10 moles of water per hour, per kilogram ofthe resultant material.
 20. The method according to claim 19, wherein vand e both equal zero, D represents an aluminum cation, d equals 1, andx represents a number of from about 1 to about 5; wherein thecrystallization comprises alkali-induced aging in an aqueous mediumcontaining an alkali metal hydroxide at a temperature of from about 60°C. to about 100° C. for a time period of from about 2.5 hours to about50 hours, and the alkali metal hydroxide is present in a concentrationof from about 1 molar to about 6 molar; and wherein the source of steamis passed continuously over the resultant material at a rate of fromabout 0.1 to about 5 moles of water per hour, per kilogram of theresultant material.